Realization of a Magnetically Tunable Slow Light Waveguide Based on Topological Modes Coupling

ABSTRACT Slow light has attracted considerable attention for its potential in optical communication, information storage and signal processing. However, simultaneously achieving a large slow light factor and a wide operational bandwidth remains challenging. In this paper, we propose a magnetically tunable slow light waveguide based on a separated topological insulator. Both the simulated and experimental results reveal the coupling between the two counter‐propagating topological edge states gives rise to a coupling dispersion curve in the bandgap. By modulating the coupling strength, the dispersion of the coupled modes can be modified rather flat, corresponding to slow‐light modes with a stopped wave point. In view of the dependence of topological edge states on ferrites’ magnetic plasmon polaritons, the slow‐light operating frequency is adjusted by the biased magnetic field. This offers a viable strategy to solve the inherent compromise between the slow‐light factor and bandwidth. Further‐more, a slow‐light rainbow waveguide with gradient biased magnetic field is proposed which permits Electro‐magnetic waves at different frequencies to stop at distinct spatial locations. Our work paves a promising avenue for exploiting of topological states in future applications.